Electrically controlled frequency reconfigurable comb type antenna is presented in this paper. Reconfigurability is achieved by placing a PIN diode in each slot of the comb type antenna. The proposed antenna has very compact size and works on 8 different bands depending upon the state and number of PIN diode (ON/OFF). Ansoft Designer 7 is used to simulate the equivalent model for the PIN diode and proposed antenna is fabricated on FR4 substrate using photolithography process. As the antenna reconfigure its resonating frequency from 1st band to 8th band, directivity increases from 3.28 to 4.02 and radiation efficiency increases from 75.3% to 93.45% due to the improvement in impedance matching at higher band.

1. Full Paper
ACEEE Int. J. on Communications, Vol. 4, No. 2, Nov 2013
Electrically Controlled Frequency Reconfigurable
Comb Type Antenna for Wireless Communication
Sonia Sharma1 and C.C. Tripathi2
sonia990@gmail.com1, tripathiuiet@gmail.com2
Department of Electronics & Communication Engineering
University Institute of Engineering and Technology (UIET)
Kurukshetra University Kurukshetra, (136119), India
Abstract— Electrically controlled frequency reconfigurable
comb type antenna is presented in this paper. Reconfigurability
is achieved by placing a PIN diode in each slot of the comb
type antenna. The proposed antenna has very compact size
and works on 8 different bands depending upon the state and
number of PIN diode (ON/OFF). Ansoft Designer 7 is used to
simulate the equivalent model for the PIN diode and proposed
antenna is fabricated on FR4 substrate using photolithography
process. As the antenna reconfigure its resonating frequency
from 1st band to 8th band, directivity increases from 3.28 to 4.02
and radiation efficiency increases from 75.3% to 93.45% due
to the improvement in impedance matching at higher band.
antennas, such as reducing the number of antennas thus
reducing the mutual interferences, complexity and cost of the
system[1-2]. Generally reconfigurability can be obtained using
many techniques such as tunable elements in the feeding
networks, adaptive matching networks, tunable filters and
tunable phase shifters[14]. Switches can been implemented
using RF-MEMS [7-10], PIN diodes [1,11,15] and varactors
[12-13]etc.
In this paper, a very compact electrically controlled
frequency reconfigurable comb type antenna is presented.
Eight pairs of PIN diode is used to achieve reconfigurability
of microstrip patch antenna. The proposed antenna works
on 8 different bands depending upon the state and number
of PIN diode (ON/OFF). There is improvement in radiation
efficiency of the antenna from 75.3% to 93.45% and directivity
3.28 to 4.02 as antenna reconfigure its resonating frequency
from 1st band to 8th band with the help of PIN diodes.
Index Terms— PIN diode, frequency reconfigurable, Micro strip
patch antenna, comb type antenna, multi band wireless
communication.
I. INTRODUCTION
In modern times, wireless devices are not limited to one
standard as they can operate at multiple frequencies. Multimode terminals have received great attention and popularity
because one can access multiple applications such as GPS,
GSM, WLAN, Bluetooth etc. in a single device[1-2]. So there
is an immense need of smart system, which can satisfy above
demands. Reconfigurable antenna is the key solution and is
a promising paradigm as it can modify its characteristics in
real time within a single structure[1-2]. The reconfigurable
characteristics of antennas are very valuable for many modern
wireless communication applications because they can
efficiently utilize spectrum and power for highly secure
multimode data transmission [1-6].
Frequency reconfigurable antennas are single antenna
that can dynamically transmit or receive multiple frequency
bands and patterns [2-6]. Such system has ability to monitor
the gaps (white spaces/unused frequency) continuously in
finite frequency spectrum occupied by other wireless
systems. These antennas can dynamically alter their transmit/
receive characteristics to operate within desired frequency
bands, thereby minimizing interference with other wireless
systems and maximizing the throughput. Frequency
reconfigurable antennas have advantages over conventional
II. THEORY
Due to many significant advantages like lightweight, low
profile, simple and inexpensive to manufacture using modern
printed-circuit technology; microstrip antenna is the best
choice for modern wireless and mobile applications [16-17].
A rectangular microstrip patch antenna of length L, width W
resting on a substrate of height h is shown in Fig. 1. The
CAD formulae for the dimension (L, W) calculation for patch
[16-17] at resonating frequency f0 on a substrate with dielectric
constant and height h are:
Effective dielectric constant
 re 
1
2
(1)
Patch width: W =
(2)
Patch length: L =
(3)
Extended length of patch due to fringing field
(4)
Sonia Sharma is Ph.D. Scholar in ECE Department, University
Institute of Engineering and Technology, Kurukshetra University,
Kurukshetra; e-mail: Sonia 990@gmail.com.
C. C. Tripathi is with Department of ECE, University Institute of
Engineering and Technology, Kurukshetra University, Kurukshetra;
e-mail: tripathiuiet@gmail.com.
© 2013 ACEEE
DOI: 01.IJCOM.4.2.16
 r 1  r 1 
h

1  12 
2
2 
W

Effective patch length: Leff = L + 2ΔL
8
(5)

2. Full Paper
ACEEE Int. J. on Communications, Vol. 4, No. 2, Nov 2013
diode pairs (a-aa, b-bb.......h-hh etc.) are introduced in between the 8 pair of teeth along the length of patch antenna as
shown in Fig 3. According to the state of PIN diode; corresponding teeth of the comb type antenna connect/disconnect from the main patch, hence electrical length of the antenna can be varied so that resonating frequency can be
reconfigured.
Fig. 1: Basic Rectangular Patch antenna
The total input impedance is given by eq. (6)
(6)
where G is conductance and given by eq.(7)
(7)
Where W = patch width and λ= resonant wavelength. If G12
is the mutual conductance between two slots, Jo is Bessel
function of first kind than
Fig 3: Electrically controlled Frequency reconfigurable comb type
antenna with PIN diode
The proposed antenna works on 8 different bands
depending upon the state and number of PIN diode. The ON
and OFF conditions of switches are realized by forward and
reverse biasing of PIN diodes. Ansoft HFSS 14 and Ansoft
Designer7 are used to simulate and model the proposed
antenna.
(8)
The above formulae are used to design a rectangular
microstrip patch antenna.
III. DESIGN APPROCH
The geometry of the proposed frequency reconfigurable
comb type antenna for wireless is depicted in Fig 2. This
antenna was printed on FR4 substrate with the dielectric
constant of 4.4 and the substrate thickness of 1.57 mm. In
this work, inset microstrip feeding technique is used.
IV. MODELLING OF PIN DIODE
The ON and OFF conditions of switches are realized by
forward and reverse biasing of PIN diode. Ideally, when a
forward bias is applied to make the PIN diode ON, the switch
Fig 2: Frequency Reconfigurable Comb type antenna
In order to get better performance like efficiency, gain,
and directivity etc. antenna should be properly matched
with feed line. The location of inset cut point is adjusted to
match with its input impedance (usually 50 ohm). The optimized parameters of proposed antenna are: length=28.2 mm,
width=36.48 mm on a ground plane of size 60x60mm2. Antenna is fed by microstrip transmission line with a metal strip
of width 3mm and length 30mm. The eight slot on the top
patch metallization are 1mm wide and 4mm long. Eight PIN
© 2013 ACEEE
DOI: 01.IJCOM.4.2.16
Fig 4: PIN diode circuit connection for diode modelling
would offer low impedance and acts as short circuit. On the
other hand, when a reverse bias is applied to make the PIN
diode OFF, it exhibits high impedance and acts as open circuit.
Working of PIN diode can be easily explained by Fig. 4 which
9

3. Full Paper
ACEEE Int. J. on Communications, Vol. 4, No. 2, Nov 2013
consists of a DC block capacitor (1µF) and a RF choke coil
(0.1µH). If diode is forward biased it can be modeled as a
resistor of 1 ohm and if diode is in reverse biased it can be
modeled as a parallel combination of 0.1µF capacitor and 25
K ohm resistor. When PIN diode is ON; insertion loss is 0.1
dB and return loss is below -15dB from 1GHz to 10 GHz as
shown in Fig. 5. When PIN diode is OFF; return loss is 0.07
dB and insertion loss is below -15dB which shows no
propagation of power from source to load terminal from 1GHz
to 10 GHz as shown in Fig. 6.
Fig 7: Return loss S11 (dB) vs. frequency for all switch condition
TABLE I:SIMULATED VALUE OF ANTENNA PARAMETERS UNDER DIFFERENT SWITCH
CONDITION
S.No
1.
2.
3.
4.
5.
6.
7.
8.
9.
Fig 5: S parameter vs. frequency when PIN diode is Forward biased
Switch
Condition
All OFF
a-aa (ON)
b-bb (ON)
c-cc (ON)
d-dd (ON)
e-ee (ON)
f-ff (ON)
g-gg (ON)
h-hh (ON)
Freq.
GHz
2.2
2.3
2.26
2.31
2.38
2.435
2.455
2.465
2.475
S11
dB
-22.44
-21.78
-20.61
-16.0474
-18.6637
-16.87
-16.49
-16.93
-16.78
Rad. Eff %
75.3
75.6
69.25
77.37
89.25
90.75
91.912
92.82
93.45
Fig. 8 shows the Radiation efficiency vs. angle for all
switch condition. Table 1 shows that return loss at different
resonating frequency under all switch condition is below 10dB.Results conclude that radiation efficiency of comb type
antenna increase from 75.3% to 93.45%.
Fig 6: S parameter vs. frequency when PIN diode is Reverse biased
V. RESULTS AND DISCUSSION
Fig. 7 shows the simulated results for return loss of Comb
Type Reconfigurable microstrip patch antenna. The overall
goal of as designed antenna design is to achieve return loss
below -10dB for good performance.
When no diode is switch ON antenna have first resonance in a frequency range of 2.2 GHz. As diode a-aa is forward biased there is conducting path between 1st teeth of
comb with the main patch hence electrical length of the comb
antenna decreases and it will resonates at higher frequency
i.e. 2.23 GHz. As the diode b-bb is forward biased than 2nd
teeth of the comb antenna merges with the main patch and
antenna will resonates at higher frequency 2.26 GHz due to
decreases in electrical length.
© 2013 ACEEE
DOI: 01.IJCOM.4.2.16
Fig 8: Rectangular plot for Radiation efficiency vs. theta for all
switch condition
So by modifying the geometry with the help of PIN diode
the resonating frequency of the patch antenna can be
reconfigure in a bandwidth of 275 MHz. The radiation pattern of comb type antenna under all switch condition is shown
in Fig. 9. Results conclude that efficiency of antenna under
10

4. Full Paper
ACEEE Int. J. on Communications, Vol. 4, No. 2, Nov 2013
all condition is greater than 70%. The simulated value for
gain and directivity of the patch antenna under different
switch condition is shown in Table 2.
TABLE II: SIMULATED VALUE OF ANTENNA PARAMETERS UNDER ALL SWITCH
CONDITION
S.No
Switch
Condition
Freq
GHz
Gain (dBm)
Directivity
1.
2.
3.
4.
5.
6.
7.
8.
9.
All OFF
a-aa (ON)
b-bb (ON)
c-cc (ON)
d-dd (ON)
e-ee (ON)
f-ff (ON)
g-gg (ON)
h-hh (ON)
2.2
2.3
2.26
2.31
2.38
2.435
2.455
2.465
2.475
31.49
31.68
34.55
32.18
33.268
33.285
33.3249
33.33
33.882
3.28
3.34
3.31
3.5
3.878
3.95
3.98
4
4.02
Directivity vs. angle under all diode condition is shown
by Fig. 10 which clearly indicate that directivity of the antenna
increases from 3.28 to 4.02.
Fig 11: Polar plot for Gain vs. theta
TABLE III: PHOTOLITHOGRAPHY T ECHNIQUE
Step
no:
Description
Equipment
Conditions
1
Prevent corners
from damaged
Substrate
cleaning
Using DI water +
Acetone+
Trichloroethylene
1 min,1 min
800C for 20 min
3
Coating of
photo resist
S1818
Pre Bake
Spin coater (Apex
instruments)
3000 rpm for 30
sec
4
Oven
1000 C for 25
min, 1150 C for
60 sec
5
Exposure
100 W i line UV
Lamp
2.30 min
6
7
Develop
Rinse in DI
water
Using 10% NaOH
Elix Millipore Lab
water Purifier
40 sec
1 min
8
Dry
Electronic dryer
Blow and dry
both side on top
9
Hard Bake
(Post Bake)
Oven
Hot Plate
10
Gain vs. angle under all diode condition is shown by Fig. 11
which clearly indicate that Gain of the antenna in all cases is
above 1 dB. Fig. 11 shows the polar plot for gain vs. theta.
Fabrication of comb antenna is done by photolithography
process. A uniform layer of S1818 photo resist is deposited
on substrate using spin coater. the mask for fabrication of
antenna transferred on the FR4 substrate by exposing the
substrate using i line UV Lamp. Pattern is formed by etching
the developed substrate using FeCl3 as shown in Fig. 12. A
sequential method for the fabrication using photolithography technique is tabulated below in Table 3.
Cutter
2
Fig 10: Rectangular plot for directivity vs. theta for all switch
condition
Substrate
cutting
Etching
30% of FeCl3
1200 C for 30
min
1200 C for 5 min
20 min
VI. CONCLUSION
Frequency Reconfigurable Comb type Microstrip Patch
antenna is successfully simulated in Ansoft HFSS 14. Ansoft
Designer 7 is used to simulate the equivalent model for the
PIN diode and proposed antenna is fabricated on FR4 substrate using photolithography process. From the simulated
results it can be easily seen that antenna reconfigure its resonating frequency in a range of 2.2 GHz to 2.475 GHz. The
© 2013 ACEEE
DOI: 01.IJCOM.4.2.16
Fig 12: Fabricated Frequency Reconfigurable Microstrip patch
a ntenna
11

5. Full Paper
ACEEE Int. J. on Communications, Vol. 4, No. 2, Nov 2013
proposed antenna has very compact size. There is improvement in radiation efficiency of the antenna from 75.3% to
93.45% and directivity 3.28 to 4.02 as antenna reconfigure its
resonating from 1st band to 8th band. Gain of the antenna in all
cases is greater than 1dB.
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© 2013 ACEEE
DOI: 01.IJCOM.4.2.16
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